Workaround the problem of creating escodegen browser bundle (#489)

[ariya]

No description provided.

[ariya]

Argh, my sed trick doesn't work on Travis CI box. Hang in there while I'm improving my sed kungfu.

[ariya]

Now it's working after I switched to Perl.

The failure on Node.js 0.10 on Travis CI has nothing to do with this pull request. It fails because of JSHint (see https://travis-ci.org/gotwarlost/istanbul/jobs/92588195 for details). For whatever reason, some files didn't pass its linting:

> istanbul@0.4.0 pretest /home/travis/build/gotwarlost/istanbul
> jshint index.js lib/ test/ && ./download-escodegen-browser.sh

test/browser/test-browser-instrumentation.js: line 57, col 13, 'server' was used before it was defined.
test/browser/test-browser-instrumentation.js: line 13, col 5, 'server' is defined but never used.

test/cli/test-text-lcov-report.js: line 35, col 13, 'output' was used before it was defined.